3D hollow CoNi-LDH nanocages based MMMs with low resistance and CO2-philic transport channel to boost CO2 capture

Layered double hydroxide (LDH) bearing numerous hydroxyl groups shows high affinity with CO 2 and is promising in mixed matrix membranes (MMMs) based CO 2 capture. However, its non-porous structure limits the further improvement of CO 2 permeability. In this work, 3D hollow CoNi-LDH nanocages were developed to construct low-resistance and CO 2 -philic transport channel in MMM by in-situ etching of ZIF-67 template. The resultant material exhibits hollow structure with cavity size of about 500 nm, mesopores and micropores from LDH stacking and ZIF-67 template. The outer layered CoNi-LDH nanosheets can attract more CO 2 molecules by their abundant hydroxyl groups, resulting in an improvement in dissolution selectivity of CO 2 over N 2 . Meanwhile, the tortuous gas diffusion paths originated from 2D nanosheet stacking can further enhance the CO 2 selectivity over N 2 . Moreover, the hollow nanocages provide CO 2 molecules with fast transport path, resulting in high CO 2 permeability. As a result, compared with pure Pebax membrane and 2D LDH/Pebax MMM, all the 3D hollow CoNi-LDH/Pebax MMMs present enhanced CO 2 permeability. The 3D hollow CoNi-LDH-2h/Pebax MMM performs the highest CO 2 permeability of 135.49 Barrer, which are increased by 141.95% and 71.50% than those of the above two membranes, respectively. The selectivity of 3D hollow CoNi-LDH-2h/Pebax MMM is about 26.30% higher than that of the pure Pebax membrane. The present membrane presents comparable CO 2 capture capacity in contrast with most reported Pebax based MMMs and surpasses the Robeson upper bond. Together with the good long-term stability, the 3D hollow CoNi-LDH nanocages are believed to be a promising candidate for MMMs to improve CO 2 capture.